Electrode material and method for producing same

Abstract

An electrode material is provided in which a coating of a carbonaceous material is formed efficiently, uniformly and strongly on the surfaces of electrode active material particles, and therefore electron conductivity and the charge and discharge capacity of batteries are improved. The electrode material includes composite particles, which includes a carbonaceous substance and an electrode active material, wherein a carbonaceous material is provided on surfaces of electrode active material particles, and a standard rate constant of a redox reaction of ferrocene occurring on the surfaces of the composite particles is 1×10 −5 cm/s or more.

The invention claimed is: 
     
       1. An electrode material for lithium ion battery comprising:
 composite particles, which comprises a carbonaceous material which is generated by thermal decomposition of an organic compound, and an electrode active material which is made of a lithium phosphoric acid compound, wherein 
 the carbonaceous material forms a carbonaceous film and surfaces of electrode active material particles are coated with the carbonaceous film, 
 the coating ratio of the carbonaceous material with respect to the surfaces of the electrode active material particles is 60% or more, 
 a film thickness of the carbonaceous film is in a range of 0.1 nm to 10 nm, and 
 a standard rate constant of a redox reaction of ferrocene occurring on the surfaces of the composite particles is 1×10 −5  cm/s or more. 
 
     
     
       2. The electrode material for lithium ion battery according to  claim 1 ,
 wherein a content of carbon in the composite particles is in a range of 0.3% by mass to 8.0% by mass. 
 
     
     
       3. The electrode material for lithium ion battery according to  claim 1 ,
 wherein the composite particles are aggregates of a plurality of particles which are the electrode active material particles wherein the surface thereof is coated with the carbonaceous material. 
 
     
     
       4. The electrode material for lithium ion battery according to  claim 1 ,
 wherein the electrode active material particles include as a main component Li x A y D z PO 4 , wherein A represents one or more selected from the group consisting of Co, Mn, Ni, Fe, Cu, and Cr, D represents one or more selected from the group consisting of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y and rare earth elements, 0<x<2, 0<y<1.5 and 0≦z<1.5. 
 
     
     
       5. The electrode material for lithium ion battery according to  claim 4 , wherein, in Li x A y D z PO 4 , A is Mn and z is 0. 
     
     
       6. A method of producing the electrode material for lithium ion battery according to  claim 1 , comprising:
 preparing a slurry by mixing an electrode active material made of a lithium phosphoric acid compound or a precursor of the electrode active material, an organic compound and a surface modifier so that the slurry has a ratio D90/D10 which is in a range of 5 to 30, wherein D90 means the particle diameter at which the accumulated volume percentage is 90% in the particle size distribution of the electrode active material or the precursor thereof and D10 means the particle diameter at which the accumulated volume percentage is 10%, and wherein the surface modifier is at least one selected from the group consisting of silane coupling agents, titanate coupling agents, aluminate coupling agents, phosphoric acid-based coupling agents, carboxylic acid-based coupling agents, amino acid and surfactants; 
 generating a granulated body by spraying and drying the slurry; 
 firing the granulated body in a non-oxidative atmosphere at a temperature in range of 500° C. to 1000° C. to generate composite particles that comprise an electrode active material and a carbonaceous film formed on the electrode active material; 
 evaluating a standard rate constant of a redox reaction of ferrocene occurring on surfaces of the composite particles; and 
 confirming whether or not the standard rate constant of the composite particles is 1×10 −5  cm/s or more to obtain the electrode material for lithium ion battery. 
 
     
     
       7. The method for producing an electrode material according for lithium ion battery to  claim 6 ,
 wherein the granulated body has a structure in which electrode active material particles and a carbonaceous material are crosslinked by the surface modifier. 
 
     
     
       8. The method of producing the electrode material according to  claim 6 , further comprising:
 evaluating the coating ratio of the carbonaceous film with respect to the surfaces of the electrode active material particles of the composite particles and confirming whether or not the coating ratio of the carbonaceous film is 60% or more; and 
 evaluating a film thickness of the carbonaceous film of the composite particles and confirming whether or not the carbonaceous film is in a range of 0.1 nm to 10 nm. 
 
     
     
       9. The method of producing the electrode material according to  claim 6 , wherein the step of preparing a slurry comprises the sub steps of:
 mixing an electrode active material made of a lithium phosphoric acid compound or a precursor of the electrode active material and a surface modifier to generate a mixture thereof; and 
 mixing said mixture and an organic compound to generate the slurry. 
 
     
     
       10. The electrode material for lithium ion battery according to  claim 1 , wherein the composite particles are secondary particles. 
     
     
       11. The electrode material for lithium ion battery according to  claim 1 , wherein the composite particles are secondary particles in which carbonaceous material is interposed between the primary particles, and the surfaces of primary particles of the electrode active material are coated with carbonaceous material, and
 the carbonaceous material which coats the surfaces of primary particles of the electrode active material and the carbonaceous material which bonds the primary particles are made of the same material.